This invention relates to heat-exchanging pipes provided with ribs on an inside surface thereof for causing turbulent flow and to a method of manufacturing a heat-exchanging pipe.
Heat-exchanging pipes are utilized in many kinds of systems. For example, the pipes shown in U.S. Pat. No. 3,861,422 --McLain (Jan. 21, 1974) and U.S. Pat. No. 3,906,605--McLain (Sept. 23, 1975) are used to cool steam that is present around the ouside of the pipe by means of a current of cooling water flowing through the pipe. The pipes are formed with rod-shaped ribs along the longitudinal direction of the inside face of the pipe in order to create turbulent flow, and thereby raise the heat-exchanging efficiency of the pipe.
The heat-transmission characteristics of such heat-exchanging pipes are improved by the formation of ribs on the inner surface of the pipe by causing turbulence when the fluid collides with them the turbulence being insufficient to substantially increase pressure loss. Previously, such ribs have been made of square cross-section for the fluid to collide with them.
However the heat-exchanging pipes shown in U.S. Pat. No. 3,906,605 do not sufficiently raise the heat-exchanging efficiency for many heat exchanging pipe applications. It has become important, especially in recent years, that the efficiency of heat-exchanging pipes be further increased because they are now being used in subterranean and ocean heat generating systems where the temperature difference between inside and outside of the pipe is smaller than in conventional systems into which heat exchanging pipes have traditionally been incorporated.
Since it is difficult to perform cutting on the interior of a smooth pipe, an effective method of pipe-making is to form ribs on sheet material such as a sheet metal and then form this sheet material into a tube and weld the two side edges thereof to join them. Two known methods of forming the ribs in the sheet material are cutting and pressing.
If the ribs are formed by a cutting operation using a milling cutter or the like, considerable time is required for the cutting operation, leading to high production costs. If press working is employed, though the efficiency of the operation is high, the (square) shape of the rib cross-section is not conductive to plastic flow of the sheet material, making it difficult to achieve accurate formation of the ribs
Referring to FIGS. 1-3, there is shown a known heat exchange pipe 101 for improving a heat transmission characteristic, as shown in Japan laid open patent (Tokkosho No. 55-43360)-Itho (Mar. 27, 1978). Grooves 102, are formed on an inner surface 103 pipe 101 However, grooves 102 which are essentiallay below the inner surface o pipe 101 do not sufficiently enhance turbulence Note that forming grooves 102, as shown, leaves what are, in essence, symmetrical raised portions having lengths L.sub.o greater than bottom width l.sub.o of the grooves. Fluid flowing in pipe 101 will tend to slide over surface 103. Therefor, pipe 101 cannot produce sufficient turbulence to improve heat-transmission characteristics.
Manufacture of the FIGS. 1-3 pipe is also a problem. If this pipe were manufactured by roll forming with the axial length L.sub.o of ribs 104 being longer than l.sub.o of grooves 102 there would be an interference caused between teeth of a forming roll (not shown) and wall portions 105 of grooves 102 or ribs 104. They would tend to be deformed in manufacture.